1. Field of the Invention
The present invention relates to the microbiological industry, and specifically to a method for producing an L-amino acid using a bacterium of the Enterobacteriaceae family which has been modified to attenuate expression of the kefB gene.
2. Brief Description of the Related Art
The KefB protein encoded by the kefB gene is a potassium transporter which belongs to the CPA2 family of monovalent cation/proton antiporters. The KefB potassium efflux system is regulated by glutathione and plays a role in responding to changes in osmotic pressure and in protecting the cell from electrophile toxicity. Potassium efflux by KefB is activated by adducts formed by the reaction of glutathione with electrophilic compounds such as methylglyoxal and chlorodinitrobenzene (Ferguson, G. P. et al., Mol. Microbiol., 1993, 9(6):1297-1303). Potassium efflux mediated by KefB leads to acidification of the cytoplasm, which protects the cell from electrophile toxicity (Ferguson, G. P. et al., Mol. Microbiol., 1995, 17 (6):1025-1033; Ferguson, G. P. et al., J. Bacteriol. 1997, 179(4):1007-1012). KefB is highly similar to KefC, an additional potassium efflux system, at the level of both their primary sequences and domain organization. Despite the high degree of sequence similarity, KefB and KefC exhibit different sensitivities to the same site-specific mutations (Ness, L. S. and Booth, I. R., J. Biol. Chem., 1999, 274(14):9524-9530). In addition to KefB and KefC, an unidentified potassium efflux system exists, capable of mediating a high rate of K+ efflux (Bakker, E. P. et al., J. Bacteriol., 1987, 169 (8):3743-3749).
But currently, there have been no reports of inactivating the kefB gene for the purpose of producing L-amino acids.